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Composite Structures
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  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 0263-8223
Published by Elsevier Homepage  [3181 journals]
  • Extended layerwise method for laminated piezoelectric and composite plates
           with delaminations, cracks or debonding of a piezoelectric patch
    • Abstract: Publication date: Available online 17 November 2019Source: Composite StructuresAuthor(s): J.X. Xu, Z.G. Xiao, Y.G. Wu, D.H. Li Extended layerwise method (XLWM) is applied to the static analysis problems of laminated piezoelectric plates and laminated composite plates with a piezoelectric patch in this paper. A piezoelectric XLWM is first developed for the laminated piezoelectric plates with multiple delaminations and transverse cracks. The discontinuities of displacements and electric potential resulted from delamination are described in the assumptions along the thickness direction. In the in-plane displacement and electric potential fields, the transverse cracks are modeled by using the extended finite element method (XFEM). The coupled electromechanical variational principle is employed to derive the Euler equations, boundary conditions and finite element formulations. And then, this piezoelectric XLWM is employed to establish a coupling analysis model for the damaged laminated composite plates with a piezoelectric patch. The damaged composite plate is discretized by the XLWM as well, so the surface displacement freedoms are included into the governing equations of composite plate and piezoelectric patch. The displacement continuity and internal force equilibrium conditions at the interface of the laminated composite plate and piezoelectric patch are considered in the final governing equations.
  • Elastic stability in biaxial testing with cruciform specimens subjected to
           compressive loading
    • Abstract: Publication date: Available online 17 November 2019Source: Composite StructuresAuthor(s): M.C. Serna Moreno, S. Horta Muñoz This work presents the main aspects that should be taken into account to design biaxial experiments with cruciform specimens in the presence of compressive loading, applied on the arms of the sample by means of compression plates. The global buckling of the cruciform specimen and the local instability of the rectangular-shaped central region submitted to biaxial loading are described numerically and analytically. The analytical expressions are derived using the buckling effective lengths technique for calculating the bifurcation stress in simply supported and clamped rectangular thin-plates made of isotropic materials and ±45° angle-ply CFRP laminates. Furthermore, the influence of the arms-to-centre thickness-ratio on the compressive load that destabilises the cruciform geometry is reviewed numerically. Finally, the use of an anti-buckling device is numerically proved to reduce the risk of instabilities and to assure more reliable results. The device consists of a cross-shaped fixture that constrains the out-of-plane displacements and an optional L-shaped support in order to force the alignment of the fixture, the sample and the testing machine.
  • Prediction of shear strength and behavior of RC beams strengthened with
           externally bonded FRP sheets using machine learning techniques
    • Abstract: Publication date: Available online 16 November 2019Source: Composite StructuresAuthor(s): Omar R. Abuodeh, Jamal A. Abdalla, Rami A. Hawileh This paper presents the use Machine Learning (ML) techniques to study the behavior of shear-deficient reinforced concrete (RC) beams strengthened in shear with side-bonded and U-wrapped fiber-reinforced polymers (FRP) laminates. An extensive database consisting of 120 tested specimen and 15 parameters was collected. The resilient back-propagating neural network (RBPNN) was used as a regression tool and the recursive feature elimination (RFE) algorithm and neural interpretation diagram (NID) were employed within the validated RBPNN to identify the parameters that greatly influence the prediction of FRP shear capacity. The results indicated that the RBPNN with the selected parameters was capable of predicting the FRP shear capacity more accurately (r2 = 0.885; RMSE = 8.1 kN) than that of the RBPNN with the original 15 parameters (r2 = 0.668; RMSE = 16.6 kN). The model also outperformed previously established standard predictions of ACI 440.R-17, fib14 and CNRDT200. A comprehensive parametric study was conducted and it concluded that the implementation of RBPNN with RFE and NID, separately, is a viable tool for assessing the strength and behavior of FRP in shear strengthened beams.
  • Aeroelastic Tailoring Method of Tow-steered Composite Wing using Matrix
           Perturbation Theory
    • Abstract: Publication date: Available online 16 November 2019Source: Composite StructuresAuthor(s): Bing Zhang, Kanglong Chen, Lei Zu In this study, a computational method based on matrix perturbation theory was proposed to solve the aeroelastic sensitivity of the fibre angle of tow-steered composite wings and find the optimal local fibre paving path for aeroelastic tailoring. Firstly, the finite element model of straight fibre composite wing was created with the multilayer composite shell element in MSC/NASTRAN. Then, the flutter velocity-sensitive region with local fibre angle was determined using matrix perturbation theory. The fibre angles were carefully adjusted only in the highly sensitive region to increase the flutter velocity, and the optimal fibre paving path was obtained. Genetic algorithm based on traditional aeroelastic tailoring method was used to carry out aeroelastic tailoring for the wings of straight and curved fibre laminated plates. Calculation results of the two tailoring methods indicate that the proposed method only needs to optimise the fibre angle in a small region to achieve the same aeroelastic tailoring effect of the traditional optimisation algorithm for tow-steered composites. The obtained maximum curvature of the fibre is also greatly decreased, which effectively reduces the difficulty in the paving process of the curvilinear fibre. The designability of tow-steered composite wings can be further improved.
  • Strengthening of RC beams with externally bonded and anchored thick CFRP
    • Abstract: Publication date: Available online 15 November 2019Source: Composite StructuresAuthor(s): A. Ghani Razaqpur, Ryne Cameron, Ahmed A.B. Mostafa Premature debonding of externally bonded FRP laminate from retrofitted reinforced concrete (RC) members can lead to inefficient use of FRP and can limit the level of strength increase that can be achieved. In this investigation, π-CFRP anchors are used in an attempt to delay the onset of premature debonding and to achieve higher strength in beams retrofitted with a 1.2 mm thick and 50 mm wide CFRP laminate. This investigation consisted of testing six large scale T-beams with a 4500 mm span, 400 mm height and 500 mm flange width under four-point bending. Two beams were tested without retrofit as control beams, one beam with the laminate epoxy bonded to the beam and the remaining three beams with the laminate epoxy bonded and anchored using CFRP π-anchors. One of the beams with 30 anchors exhibited a 46% increase in the debonding load over the beam without anchors while the laminate attained a maximum strain equal to 80% of its ultimate strain capacity, a 94% increase compared to the maximum strain reached in the companion beam strengthened with only the epoxy bonded laminate. The displacement ductility ratio of the latter beam at debonding exceeded 4. The results demonstrate the π-anchoring system effectiveness and a feasible way for efficiently utilizing strong and thick laminates in strengthening RC members.
  • Bend-free Design of Ellipsoids of Revolution using Variable Stiffness
    • Abstract: Publication date: Available online 15 November 2019Source: Composite StructuresAuthor(s): Shahrzad Daghighi, Mohammad Rouhi, Giovanni Zucco, Paul M. Weaver Shells are commonly used in many structural applications due to their high specific load carrying capabilities. One of the most interesting features of shell structures is that they can resist external transverse loads by developing membrane stresses in the small deformation regime yet, in general, also generate inefficient bending deformations and stresses. In this study, a composite ellipsoid shell of revolution, under internal pressure, is designed for zero bending and curvature change. To this end, the stiffness properties of elliptical composite shell structures are tailored by fibre steering. A new definition for a bend-free state, independent of internal pressure, is presented. Based on this definition, the internal pressure-induced bending state of an isotropic ellipsoidal shell of revolution is compared with its tailored composite counterpart. Results show that up to a specific level of ellipticity, a bend-free state is achievable by fibre steering in elliptical composite shells of revolution. Finally, a failure study is performed to assess the potential improvement of the maximum allowable internal pressure by bend-free design.
  • Experiment, modeling and simulation of bypassing holes in composites
    • Abstract: Publication date: Available online 14 November 2019Source: Composite StructuresAuthor(s): Stefan Hartmann, Ali Kheiri Marghzar, Rose Rogin Gilbert, Woramon Pangboonyanon, Dieter Meiners This article discusses modeling aspects of fiber circumplacement around a hole using continuous functions. Here, spatially inhomogeneous transversal isotropy is formulated on the basis of patches using B-spline approaches generating the fiber orientation. For this purpose, experiments with different fiber orientations and “hole”-concepts are provided for both the identification of material parameters as well as for model validation. The validation examples are a plate with uniform fiber distribution, where the hole is drilled after the production process, and a plate with circumplacement around the hole, where the fibers are bypassed before the matrix material is injected. The entire numerical problems are treated using finite elements. Furthermore, the material parameters are identified using – within a least-square approach – the combination of finite element simulations and optical results of a digital image correlation system.
  • Mesoscale finite element analysis of cracked composite laminates under
           out-of-plane loads using 3D periodic boundary conditions
    • Abstract: Publication date: Available online 14 November 2019Source: Composite StructuresAuthor(s): D. Garoz, M. Hajikazemi, T.D. Dinh, W. Van Paepegem The behavior of composite materials under out-of-plane loads is strongly affected by the presence of transverse ply cracks. The cracks perturb the distribution of stresses leading to large out-of-plane shear stiffness reductions. It is crucial to include these effects in the damage material models to improve their accuracy. Therefore, the stress transfer and stiffness reduction in cracked laminates have been studied with a mesoscale finite element model (FEM) under general in-plane, out-of-plane normal and shear loads. A symmetric laminate containing ply cracks in a single orientation has been considered under the hypothesis of periodicity using a novel relaxed three-dimensional formulation of Periodic Boundary Conditions (PBCs). The local stresses have been verified versus different analytical and numerical methods. In addition, the degraded effective thermo-elastic constants involving out-of-plane properties have been calculated as a function of crack density. Both uniform and non-uniform distributions of cracks have been considered for different lay-ups including angle-ply and unbalanced laminates. The effect of contact between the crack surfaces has been studied for specific loading conditions. It is shown that a single formulation based on three-dimensional periodic boundary conditions is sufficient to determine the interfacial stresses and the complete thermo-elastic constants under in-plane and out-of-plane loads accurately.
  • Constructing various simple polygonal tensegrities by directly or
           recursively adding bars
    • Abstract: Publication date: Available online 13 November 2019Source: Composite StructuresAuthor(s): Xu Yin, Yue Li, Li-Yuan Zhang, Guang-Kui Xu As an important type of tensegrities, polygonal tensegrities and their assemblies/variants hold various applications in, such as, architectures, robotics, and metamaterials. We here propose two methods (direct and recursive methods) to construct the topologies of simple polygonal tensegrities by directly and recursively adding bars, respectively. In the design of a simple 2n-polygonal topology using the direct method, we arrange 2n strings and 2n nodes according to the edges and vertices of simple 2n-polygon, and then add n bars between each two of un-neighboring nodes. In the same topological design using the recursive method, we construct the topology of quadrilateral tensegrity as a start, then add one bar to generate a hexagonal topology, and repeat this operation until the total number of added bars reaches n. These two methods yield exactly the same configurations, showing that the total number of simple polygonal topologies increases exponentially with the number of bars. Surprisingly, there exist almost 100 million simple 22-polygonal topologies. Finally, we validate both numerically and experimentally that each of our designed topologies can produce a stable tensegrity configuration without external loads. This work sheds light on the topological features and mechanical characteristics of polygonal tensegrities, which help broaden their application scenarios.
  • Regularized Least Squares for the Building of a Sizing Criterion Based on
           Damage Mechanics
    • Abstract: Publication date: Available online 12 November 2019Source: Composite StructuresAuthor(s): Orestis Friderikos, Emmanuel Baranger, Damien Guillon Utilization of the building-block approach for the design of composite parts emerged from the need to develop a true understanding of the complex composite structural response through experimentation and analysis. The present work aims to provide a numerical counterpart to the expensive experimental testing of advanced composite laminate structures. This detailed analysis can be fully integrated into the building-block approach to enhance its capability to examine the full-scale structural behavior and improve its reliability. To this end, a Virtual Testing Analysis (VTA) based on the structural decomposition into a number of complicated laminates is introduced for determining premature damage evolution. VTA augment FEM with a hierarchical procedure which goes down to the meso-scale where a detailed modeling of each component is examined using non-linear FEM. Design of Experiments is utilized for an optimal sampling of the design space related to the laminate subcomponents. Linear least squares regression using Tikhonov regularization (L2-norm penalty function) and Truncated Singular Value Decomposition (TSVD) are used to combat overfitting and stabilize possible ill-conditioned matrix inverse problems. Furthermore, a Multi-Stage Least Squares methodology is implemented as an alternative approximation which utilizes a separation of the design variables into sets. This method yields optimal solutions in each subspace in a hope to obtain the final global optimal solution from the composition of locally optimal solutions. Performance and efficiency is evaluated both for training and validation data using error measures based on the residuals. Preliminary results showed acceptable accuracy for the linear least squares and Multi-Stage Least Squares methods. An important key aspect of VTA is that off-line computations for the advanced laminates can be stored and used for different full-scale structures as a simple failure criterion.
  • Geometrically nonlinear analysis of CNT-reinforced functionally graded
           composite plates integrated with piezoelectric layers
    • Abstract: Publication date: Available online 11 November 2019Source: Composite StructuresAuthor(s): S.Q. Zhang, Y.S. Gao, G.Z. Zhao, Y.J. Yu, M. Chen, X.F. Wang The paper develops a geometrically nonlinear finite element model with large rotation based on the first-order shear deformation (FOSD) hypothesis for static and dynamic analyses of piezoelectric integrated carbon nanotube reinforced functionally graded (P-CNT-FG) composite structures. A constant electric field distribution through the thickness of plate are considered. An eight-node quadrilateral plate element with five mechanical degrees of freedom (DOFs) and one electric degree of freedom is developed for finite element analysis. Four typical forms of CNT distributions are included in the model, namely uniform, V-shaped, O-shaped, and X-shaped distributions. The nonlinear model considers fully geometrically nonlinear strain-displacement relations and large rotation of the shell direction of plate. Using the Hamilton’s principle, a nonlinear dynamic model including dynamic and sensory equations is obtained. The proposed nonlinear model is validated by a frequency analysis of a simply supported P-CNT-FG composite plate. Furthermore, the effects of various parameters on the static and dynamic behavior are investigated, e.g. CNT-reinforcement orientation, CNT distribution, the number of laminate layers and volume fraction.
  • Characterizing the constitutive response of plain-woven fibre reinforced
           aerogel matrix composites using digital image correlation
    • Abstract: Publication date: Available online 11 November 2019Source: Composite StructuresAuthor(s): Xiao-hui Ji, Zi-qing Hao, Li-jun Su, Ti-ren He, Liu Liu The paper presents an experimental investigation of the constitutive behavior for plain-woven fibre reinforced silica aerogel matrix composites under a complex in-plane stress state using digital image correlation technique. Specimens were subjected to in-plane on-axis, off-axis tension and shear loadings. The material exhibits significantly nonlinear stress-strain behaviour under off-axis tension and shear loadings. Deformation mechanism of the composite material has been proposed using FEM analysis of representative volume cell qualitatively. It is proposed that nonlinear couplings of the stress and strain components may result from a combination of stress-free surface, heterogeneity and interaction of the woven fibre bundles and aerogel matrix for thin specimen under a complex stress state, even though no damage initiates in the material. The experimental results were subsequently used to develop a constitutive model based on general formulation of complementary strain energy density. The material constitutive parameters were extracted from calculated stress and measured strain using multi-variable linear least square regression. The performance of the constitutive model has been demonstrated by comparison with the off-axis tensile experimental results.
  • Stiffness degradation effects on disk-shaft connection behavior of a
           three-dimensionally carbon-fiber-reinforced composite rotating disk
    • Abstract: Publication date: Available online 11 November 2019Source: Composite StructuresAuthor(s): N. Hiroshima, H. Hatta, J. Yoshimura, K. Goto, Y. Kogo, S. Wakayama High-speed rotation tests of a three-dimensionally reinforced annular disk were conducted with specimens, but were suspended at a speed below that predicted for disk fracture by high-amplitude vibrations. As described herein, the vibration source was assumed to be disk stiffness degradation. This study examined the validity of this mechanism. First, laser devices were used to measure elastic displacement at the disk periphery and to estimate global disk stiffness. Second, static ring burst tests using circular ring specimens machined from composite disks were conducted to evaluate the circumferential stiffness. Compression tests were done using rectangular parallelepiped specimens for the radial stiffness. Results show that the circumferential stiffness was 67% of the prediction by the rule of mixture. The radial stiffness was 85% of that. Locally wavy carbon fiber bundles were responsible for stiffness degradation. Stiffness degradation effects on the shaft–disk connection were specifically examined based on those results.
  • A stabilized node-based smoothed radial point interpolation method for
           functionally graded magneto-electro-elastic structures in thermal
    • Abstract: Publication date: Available online 11 November 2019Source: Composite StructuresAuthor(s): Shuhui Ren, Guangwei Meng, Jiye Wang, Liming Zhou, Hongwei Zhao It is well-known that the standard finite element method (FEM) has the disadvantage of ‘overly-stiff’ and could not offer reliable enough solutions. We proposed a novel stabilized node-based smoothed radial point interpolation method (SNS-RPIM) to analyze the free vibration and the behavior of functionally graded magneto-electro-elastic (FGMEE) devices under mechanical and thermal load, which cured the ‘overly-soft’ and temporally instability of traditional NS-RPIM. The gradient variance items associated with the field nodes are applied to construct the system stiffness matrix. The detailed numerical study has shown the superiority of the proposed method. SNS-RPIM performs well in solving static magneto-electro-thermo-elastic (METE) multi-physics coupling field problems, which validates the accuracy, convergence of the proposed method. Moreover, SNS-RPIM is less insensitive to mesh distortion than FEM and NS-RPIM. The advantages mentioned above make SNS-RPIM very helpful for the design of the actual intelligent devices.
  • The influence of mode II test configuration on the cohesive law of bonded
    • Abstract: Publication date: Available online 9 November 2019Source: Composite StructuresAuthor(s): S. Abdel Monsef, M. Pérez-Galmés, J. Renart, A. Turon, P. Maimí This paper aims to discuss the effect mode II type tests have on the cohesive law of bonded joints. For this reason, an objective inverse method has been developed to extract the cohesive law for experimental load-displacement data using an analytical procedure to represent the fracture process zone of mode II tests. The method is implemented on the more popular and standardized mode II tests: End-Notched Flexure and End-Load Split. The analysis of the experimental data shows that the cohesive law is independent of the test type. In addition, the obtained fracture toughness calculated by integrating the cohesive law shows good agreement with the J-integral method.
  • Study on the stab resistance mechanism and performance of the carbon,
           glass and aramid fiber reinforced polymer and hybrid composites
    • Abstract: Publication date: Available online 9 November 2019Source: Composite StructuresAuthor(s): Jinsil Cheon, Minwook Lee, Minkook Kim In this study, stiff stab-resistant materials for riot shields were developed by using fiber reinforced polymer composites (FRPs) made of three different types of fibers: carbon, glass and p-aramid. The stab resistance of the FRPs were investigated with respect to the thickness and types of reinforced fibers according to the U.S.A. National Institute of Justice (NIJ) standard. Hybrid composites were then developed to compensate for the weaknesses of each FRP, and the stacking sequences were optimized. The mechanisms of the stab resistance and the blade penetration for each FRP were investigated via static stab compressive tests. Additionally, the failure mode and fracture topography after the stab resistance tests were obtained using a micro-CT scanner.
  • Reliability analysis of composite wind turbine blades considering material
           degradation of blades
    • Abstract: Publication date: Available online 9 November 2019Source: Composite StructuresAuthor(s): H.M. Su, T.Y. Kam In this study, a set of analytical methods was proposed to evaluate the reliability of composite wind turbine blades after material aging, and to improve the blade structure strength to enhance its reliability. Because, the material aging will occur when the blade is affected by the external environment for a long time, consequently, time is an extremely important factor in reliability. Therefore, it is necessary to simulate the effect of environment on materials by aging experiments, so as to obtain the relationship between time, material strength and material constant.The reliability evaluation method used in this study is the direct integration method, which can quickly evaluate the reliability of blades degraded by materials. Because the reliability of the unmodified blade impossible be more than 98% after 20 years, it is necessary to improve the blade and then evaluate the reliability. The weight of the improved blade increased by only 8.57%, but the wind speed of buckling could be delayed by 32.47%, and the reliability could be more than 99% after 20 years, so the improved method meets the demand.
  • Shear behaviour of steel-UHPC composite beams in waffle bridge deck
    • Abstract: Publication date: Available online 8 November 2019Source: Composite StructuresAuthor(s): Jin-Song Zhu, Yong-Guang Wang, Jia-Bao Yan, Xiao-Yu Guo This paper firstly proposed the steel-UHPC composite beam in waffle bridge deck system. Then, the shear behaviour of steel-UHPC composite beams in waffle bridge deck system were studied through two-point loading tests on six large scale specimens. The influences of shear span, depth of the rib, and width of the UHPC waffle slab were studied in this testing program. The experimental results reported the typical flexure and shear mode of the composite beam, and their respective ultimate strength behaviours in terms of load versus deflection (or strain) curves and load-transferring mechanism. The test results also showed that shear spans changed the failure mode of steel-UHPC composite beams. The height of the rib in the waffle slab acted less importantly than the thickness of slab on improving shear resistance of the composite beam. Theoretical models were also developed to predict the ultimate bending and shear resistance of steel-UHPC composite beams. The validations of the predictions against the reported six test results showed that the developed theoretical models offered conservative estimations on shear resistance, but more accurate estimations on flexural bending resistance.
  • Finite element investigation of fatigue performance of CFRP-strengthened
           beams in hygrothermal environments
    • Abstract: Publication date: Available online 8 November 2019Source: Composite StructuresAuthor(s): Y.L. Wang, X.Y. Guo, P.Y. Huang, K.N. Huang, Y. Yang, Z.B. Chen The effectiveness of reinforced concrete (RC) external bonded with carbon fiber reinforced polymer (CFRP) laminates is bound by the negative effect of hygrothermal environment and cycle load. In order to prove the durability of CFRP-strengthened RC beams in hygrothermal environment, this paper concentrates on a numerical and experimental research of the failure modes and fatigue life of CFRP-strengthened RC beams under the coupling action of hygrothermal environment and cyclic load. Considering that two main failure modes of CFRP-strengthened RC beams are debonding of CFRP-concrete interface and main reinforcement fracture, the failure criterion of interface debonding and main reinforcement are involved in finite element method (FEM). Based on the fatigue damage accumulation, the failure mode which occur first can be predicted. The results show that the main failure mode of CFRP-strengthened RC beams in indoor environment is main reinforcement fracture. With the increase of temperature and humidity, interface debonding become the main failure mode. The fatigue life corresponding to failure mode under different hygrothermal environments can be calculated, which is in good agreement with experimental results.
  • Durability of glass fibre-reinforced polymer (GFRP) bars embedded in
           concrete under various environments. I: Experiments and analysis
    • Abstract: Publication date: Available online 8 November 2019Source: Composite StructuresAuthor(s): Daoguang Jia, Qingyong Guo, Jize Mao, Jianfu Lv, Zailin Yang This paper presents the tensile strength of glass fibre-reinforced polymer (GFRP) reinforcing bars embedded in concrete that is exposed to tap water, saline solutions and ambient humidity under accelerated conditions. These conditions were used to simulate the effect of river water, seawater or atmospheric moisture on the GFRP bars. In addition, the electrical impedance method was employed to evaluate the water content at different depths of a concrete cover under a variety of ambient humidity conditions. The effects of seawater, water-to-cement ratio (W/C) of the concrete cover, environmental humidity and cover depth were studied. The results revealed that the GFRP bars embedded in concrete exhibited a substantial strength loss when exposed to tap water or high ambient humidity. The degradation of concrete-wrapped GFRP bars immersed in saline solution could be different. This discrepancy is due to the variation of the degradation mechanism after exposure to chloride ions and is related to the cover depth. The depth of the concrete cover also had an evident influence on the durability results of GFRP bars subjected to various humid environments. Furthermore, reducing the W/C of the concrete cover had negative effects on the GFRP reinforcing bars.
  • Blast Performance of a Bio-mimetic Panel based on the Structure of Nacre
           – A Numerical Study
    • Abstract: Publication date: Available online 8 November 2019Source: Composite StructuresAuthor(s): Abdallah Ghazlan, Tuan Ngo, Van Tu Le, Tuan Nguyen, Alex Remennikov Nacre, the tough protective layer of a mollusk seashell, has a fracture toughness that is several orders of magnitude higher than brittle aragonite, a ceramic that accounts for 95% of its composition. As such, it possesses characteristics that may be highly beneficial for protective structural applications. In this research, several structural characteristics from nacre’s brick and mortar-like microstructure are mimicked with the goal of enhancing the stiffness and fracture toughness of a monolithic ceramic panel under blast loading. These features include the mineral bridges connecting the adjacent brick-like tablets for enhancing the stiffness of the panel, the multi-layered structure for enhancing its toughness via cracking bridging mechanisms and the growth bands between the nacreous tablet layers for deflecting cracks. The results from the numerical simulations showed that the nacre-like panel possesses superior energy dissipation over the monolithic ceramic panel, which thereby reduces the reaction forces transmitted to the supports and mitigates catastrophic failure. This has positive implications in terms the capability of fine tuning the structural characteristics an armor system for defeating impulsive loads by employing the principles adopted in the microstructure of a natural armor system.
  • Interactions of monitored factors upon tensile glue shear strength on
           laser cut wood
    • Abstract: Publication date: Available online 7 November 2019Source: Composite StructuresAuthor(s): Milan Gaff, Fatemeh Razaei, Adam Sikora, Štěpán Hysek, Miroslav Sedlecký, Gianluca Ditommaso, Roberto Corleto, Gourav Kamboj, Anil Sethy, Michal Vališ, Kamil Řipa Over recent decades, laser technology is at the forefront of material processing and in the near future, probably, it can be considered as a replacement for traditional techniques such as sawing. This paper reports the effect of monitor factors (cutting methods, moisture content at laser cutting, surface waviness and roughness) on tensile shear strength of glued layered wood. The process of laser cutting was applied on beech (Fagus sylvatica L.) and oak wood (Quercus robur L.). The quality of the surfaces resulted from laser cutting was measured by contact type surface profilometer. To ascertain the bonding behavior, laser cut surfaces were bonded with polyvinyl acetate adhesive and tensile glue shear strength was investigated on the bond-line. The results were compared with the results on saw cut samples. The test results revealed significant influence of monitored factors on the tensile shear strength of glued joints. The tensile glue shear strength values on laser-cut wood samples were significantly lower than those on saw cut samples.
  • Functionally graded “Ti-base + (Ta, Ta2O5)-coatings” structure and
           its production using induction heat treatment
    • Abstract: Publication date: Available online 7 November 2019Source: Composite StructuresAuthor(s): Marina Fomina, Vladimir Koshuro, Aleksandr Shumilin, Aleksey Voyko, Andrey Zakharevich, Aleksandr Skaptsov, Aleksey Steinhauer, Aleksandr Fomin On the surface of the “Ti-base + Ta-coating” layered system, tantalum oxide coatings were obtained by induction heat treatment (IHT) within 600–1600 °C for 1–120 s. It was established that in the entire range of temperature and duration of IHT, the highest oxide with an oxygen concentration C[O] = 70.35–72.48 at.% was formed on tantalum. An oxide coating without cracks having an average grain size DG = 170–340 nm and pore size DP = 130–150 nm was formed at T = 1000–1050 °C. With an exposure time t = 30–120 s in the temperature range from 850–900 to 1000–1050 °C, high hardness values ​​about 39–47 HRA (105–135 HV) for the tantalum layer and about 69–84 HRN15 (240–495 HV) for the near-surface layer were noted. These samples also had a superhard oxide coating with H0.01 = 55.27±16.00 GPa and H0.1 = 39.09±13.10 GPa. The results of the study of these samples showed that high microhardness ​​of 1579±537 HV0.2 combined with high Rockwell hardness and low defectiveness of the oxide coating allowed the creation of a mechanically stable “Ti-base + (Ta, Ta2O5)-coating” layered system.
  • Orientation optimization in anisotropic materials using gradient descent
    • Abstract: Publication date: Available online 7 November 2019Source: Composite StructuresAuthor(s): Yang Shen, David Branscomb The rapid advancement in additive manufacturing makes it feasible to manipulate material orientation locally to construct optimized structure. The remaining question becomes: how to find such material orientation distribution to minimize/maximize properties of a additively manufactured structure' Despite much research has been done to solve this problem, they all have constraints and especially lack the study of optimization algorithm at the fundamental level. In this work, the objective is to use gradient descent method to find the optimal distribution of material orientation for anisotropic materials to minimize compliance under plane stress condition. We propose a rationalized formula referred to as normalized gradient by maximum (NGM) to calculate step length. Gradient descent method has been demonstrated at the fundamental level that it is well suited for solving this problem provided that a proper step length can be calculated. NGM calculates step length at nearly no extra cost to guarantee that iterative process convergences to a local/global extreme. NGM method is validated by a tensile and shear condition.
  • An approximate solution for vibrations of uniform and stepped functionally
           graded spherical cap based on Ritz method
    • Abstract: Publication date: Available online 7 November 2019Source: Composite StructuresAuthor(s): Cong Gao, Fuzhen Pang, Haichao Li, Lei Li Based on Ritz method, the vibration approximate solutions of uniform and stepped functionally graded (FG) spherical cap are carried out in this paper. The first-order shear deformation theory (FSDT) is used to derive energy expression. The selections of displacement functions are based on domain decomposition approach, in which the unified Jacobi polynomials are introduced to represent the displacement functions component along axial direction. In addition, the standard Fourier series still denote the displacement functions component along circumferential direction. The various boundary conditions are simulated by applying spring stiffness method. Then the Ritz method is employed to obtain the final results. The solutions of the same condition are compared with those obtained by finite element method (FEM) and published literatures to validate the present method. The results exhibit that the current approach has the advantages of high solution accuracy and fast convergence. On this basis, the numerical results concerning the effects of geometric parameters and boundary conditions on the vibration responses of the structure are also considered.
  • Dynamic delamination on elastic interface
    • Abstract: Publication date: Available online 6 November 2019Source: Composite StructuresAuthor(s): Tianyu Chen, Christopher M. Harvey, Simon Wang, Vadim V. Silberschmidt The dynamic energy release rate (ERR) is derived for a delamination on the interface between a partially supported vibrating beam and an elastic foundation, with a time-dependent displacement applied to the beam’s free end. The configuration may represent, for example, the dynamic delamination of a laminated composite, or the cracking of a typical adhesively bonded composite joint. The developed theory is completely analytical and applicable to both symmetric double cantilever beams (DCBs) and thin layers on thick substrates. It was discovered that the dispersive propagation of flexural waves should be considered in order to capture contributions to the ERR from higher-order vibration modes. The developed theory is verified using finite-element-method (FEM) simulations and they are found to be in excellent agreement. This work will be useful to characterize the dynamic fracture toughness of layered materials in DCB tests, and to determine the fracture behavior of engineering structures under dynamic loads. Furthermore, the partially supported beam’s elastic foundation is relevant for the study of crack process zones, which are usually analyzed using the FEM and the cohesive-zone model. The potential applications of this study include determining the dynamic fracture toughness for crack initiation in laminated composite DCBs and adhesively bonded structures.
  • Compressive behaviour of concrete-filled carbon fiber-reinforced polymer
           steel composite tube columns made of high performance concrete
    • Abstract: Publication date: Available online 6 November 2019Source: Composite StructuresAuthor(s): Krzysztof Ostrowski, Mateusz Dudek, Łukasz Sadowski The confinement of concrete-filled steel columns (CFT) with carbon fiber-reinforced polymer (CFRP) has been extensively studied in recent decades due to their significant applications for the strengthening purposes or construction of composite structures. A CFT column consists of a steel tube and inner-filled concrete, where the steel tube is used as a form and confinement of the concrete, with the concrete being the core that prevents buckling of the tube. Due to the development of concrete technology, high performance concrete (HPC) is increasingly used as the internal material of CFT. However, CFT columns are susceptible to local buckling and constant confining stress after yielding of the steel tube. This is why concrete-filled carbon fiber-reinforced polymer steel composite tubes (CFCT) have been considered. The key parameter, which determines load-carrying capacity, and axial and transverse deformation is the number of CFRP layers. The test results showed that local buckling of the steel tube can be effectively eliminated and that the compressive strength of CFCT is enhanced by the external confinement. It has been shown that the stress-strain characteristic depends on confinement pressure. This paper also discusses damage patterns and presents analysis of limit load capacity based on both laboratory experiments and numerical calculations.
  • Micromechanical Analysis of Damage Mechanisms under Tension of 0o-90o
           Thin-ply Composite Laminates
    • Abstract: Publication date: Available online 6 November 2019Source: Composite StructuresAuthor(s): M. Naderi, N. Iyyer A micromechanical model is used to investigate ply thickness effect on damage evolution of thin-ply laminate carbon fiber reinforced laminate under transverse tensile load. Representative volume element (RVE) for 900 lamina are constructed and sandwiched between two homogenized zero degree plies. Four different thicknesses for 90o RVEs including 30, 60, 90, and 120 μm are considered for analysis. The three dimensional (3D) computational micromechanics are combined with augmented finite element method (AFEM) to provide high-fidelity results of damage evolution. Random arrangement for fibers and normal distribution for interface toughness and strength are considered within RVEs. Damage evolution in different RVEs under tensile loading are discussed and compared. The results show that decreasing 90o lamina thickness alters damage progression mechanism and suppresses cracking within matrix loading. A detailed comparative discussion on the influence and importance of material parameters as well as void/defects on the process of cracking are given.
  • Experimental and numerical study of CFRP protective RC piers under contact
    • Abstract: Publication date: Available online 6 November 2019Source: Composite StructuresAuthor(s): Lu Liu, Zhouhong Zong, Chao Gao, Sujing Yuan, Fan Lou In the wake of the event of September 2001, the increasing terrorist attacks have been a destabilizing threat around the world. Public infrastructure, such as tall buildings and traffic facilities, have become attractive bombing targets for terrorists. Crucial bridges subjected to great destruction from bomb attacks can contribute to casualties, property loss and interruption of the transportation system. Bridge piers are the main axial bearing components that are common in bridge construction, and it can readily suffer damage under blast loading. Therefore, it should be necessary to explore protective measures for reinforced concrete (RC) piers to resist blast loading. In this paper, carbon fibre reinforced polymer (CFRP) is chosen to protect RC piers under contact explosion. Five piers, consisting of two unprotected piers and three CFRP protective piers, are constructed and the explosion testing is conducted in the field. Additionally, finite element models of CFRP protective piers are built, considering the contact between concrete and CFRP as well as the anisotropy of CFRP composite material. The models are calculated using the Arbitrary Lagrange Euler (ALE) algorithm and validated by experimental acceleration as well as damage extent. Then, the damage development and CFRP protective effect for RC piers are further analysed. Finally, all specimens experience local failure under contact explosion and the simulative models are proved accurate for depth analysis.
  • Interlayer contact mechanism of the frictional behavior of glass-fiber
           woven fabrics and improvements of winding characteristics
    • Abstract: Publication date: Available online 24 September 2019Source: Composite StructuresAuthor(s): Zhong Xiang, Yang Liu, Xiangqin Zhou, Zhenyu Wu, Xudong Hu Interlayer friction is an important factor in producing rolls of glass-fiber woven fabric and strongly depends on the fabric structure and fabric interlayer contact mechanism. This paper investigates the effect of the initial contact state on the fabric/fabric friction coefficient by adjusting dislocations along circumferential and axial directions with a Capstan-based test setup. Results reveal that the maximal friction coefficient is approximately proportional to the height gradient between two adjacent yarns, while the minimal friction coefficient is less sensitive to the fabric structure. Moreover, a dislocation between fabric layers reduces both the maximal static and dynamical friction coefficients, and actively reciprocating a dislocation along the axial direction is an effective way of avoiding the interlayer friction from remaining at a low level. A dislocating mechanism is developed and introduced to a commercial fabric winding machine to verify the effectiveness of the proposed method in improving winding quality.
  • A critical review on 3D printed continuous fiber-reinforced composites:
           History, mechanism, materials and properties
    • Abstract: Publication date: 15 January 2020Source: Composite Structures, Volume 232Author(s): S M Fijul Kabir, Kavita Mathur, Abdel-Fattah M. Seyam Three-dimensional printing (3DP), interchangeably termed as additive manufacturing, is an emerging technology for creating myriad objects with numerous design flexibilities by sequential layering. The research revolving 3DP to develop different high-performance materials is in its young stage and burgeoning exponentially throughout the globe. The widest applications of 3DP technology are found in automobile, aerospace, building, metal and alloy, electronic and biomedical fields. Recently, the opportunity to use fiber as reinforcement in the plastic resin of 3D printed model has contributed significantly to the improvement of mechanical performances of 3D printed composites. In the present review, along with introducing brief history of 3DP, mechanism of embedding different continuous fibers into different plastics and their microstructural and mechanical properties including predicting models have been critically reviewed. Additionally, based on the limitations of current technology future research directions have been defined.Graphical abstractGraphical abstract for this article
  • Analysis of stress concentration phenomenon of cylinder laminated shells
           using higher-order shear deformation Quasi-3D theory
    • Abstract: Publication date: 15 January 2020Source: Composite Structures, Volume 232Author(s): Tran Ngoc Doan, Do Van Thom, Nguyen Truong Thanh, Phan Van Chuong, Nguyen Chi Tho, Nguyen Tri Ta, Hoang Nam Nguyen This paper presents the stress concentration phenomenon at the points with force jumping, structural jumping and sudden changes of boundary conditions of cylinder laminated shells. The three-dimensional linear elastic equation is transformed into the two-dimensional linear elastic equation of the cylinder laminated shell by using the variational method and analyzing the displacement field into a polynomial function sequence according to the shell thickness. Equilibrium equations are achieved corresponding to the case of analyzing the displacement field into the cubic function. Based on established equations, we study the jumping zone phenomenon of the stress field in the structure. Effects of boundary conditions, the relative thickness and the relative length of the shell are investigated. Then, the application areas of each case based on the computed results are figured out when using these types of structures in engineering practice.
  • Fabrication and application of electrically conducting composites for
           electromagnetic interference shielding of remotely piloted aircraft
    • Abstract: Publication date: 15 January 2020Source: Composite Structures, Volume 232Author(s): Roman Turczyn, Katarzyna Krukiewicz, Andrzej Katunin, Jan Sroka, Przemysław Sul Electromagnetic interference (EMI) is the phenomenon occurring in remotely piloted aircraft systems, especially in the radio-frequency band emitted by motors and power supplies, that needs to be shielded in order to avoid disturbances in communication signals. This paper presents a solution to this problem in the form of EMI shielding housing based on electrically conducting epoxy resins filled with polyaniline (PANI) and polypyrrole (PPy). For this purpose, PANI and PPy were synthesized and characterized to achieve effective EMI shielding of the resulting composite materials and reinforced with carbon fabric. Optimized materials were then used as EMI shielding housing for a remotely piloted aircraft system. The obtained results of electromagnetic compatibility tests showed the ability of damping of both manufactured composites, especially in the range of 30–35 MHz, where damping was the highest, with the average difference between conducting and non-conducting composites of ca. 20 dBµV/m.
  • Experimental characterization, analytical and numerical investigations of
           metal/polymer/metal sandwich composites – Part 2: Free bending
    • Abstract: Publication date: 15 January 2020Source: Composite Structures, Volume 232Author(s): Mohamed Harhash, Rose Rogin Gilbert, Stefan Hartmann, Heinz Palkowski In this article, we continue the investigations on the forming behavior of the steel/polymer/steel (SPS) sandwich composites as introduced in Part 1 [1]. In this paper, the main focus lies on bending conditions, validated by analytical and numerical methods. A wide variety of SPS layer configurations and thicknesses were tested under three-point bending conditions considering different bending angles (60, 90 and 150°) and different punch radii (1.5, 3, 6 and 12 mm). The results are validated in terms of the bending forces, springback degree, strain field distribution, and thickness reduction, where a good matching between the numerical and analytical results with the experimental ones was reached.
  • Computationally-efficient homogenization and localization of
           unidirectional piezoelectric composites with partially cracked interface
    • Abstract: Publication date: 15 January 2020Source: Composite Structures, Volume 232Author(s): Qiang Chen, Guannan Wang The homogenized and localized responses of unidirectional piezoelectric composites with partially cracked interface are investigated in this contribution. To simulate the electro-elastic fully-anisotropic constitutive behavior, a micromechanical multiphysics finite-element model is developed through adopting higher-order internal trial functions. The generated results are validated against the independently-developed generalized Eshelby solution with piezoelectric effects, a comparable finite-volume (FV) technique, and ABAQUS simulations with excellent agreement. More importantly, the present work investigates thus-far little explored effects of several microstructural details including the fiber/matrix property ratio, an elliptical inclusion, multiple periodic inclusions, as well as the crack length and poling direction, on either effective properties or local stress/electric field distributions. It is also demonstrated that the present model is advantageous to commercial finite-element packages in two aspects. Firstly, the periodic boundary conditions of the nodal displacements and electric potential are enforced explicitly. Secondly, the ability to generate a complete set of homogenized moduli with two-dimensional architectures sets the present model apart from the readily available commercial codes that require a three-dimensional unit cell analysis.
  • A stress function based viscoelastic model for relaxation of free edge
           stresses in composite laminates
    • Abstract: Publication date: Available online 23 October 2019Source: Composite StructuresAuthor(s): Bin Huang, Jianbin Chen, Lichen Hua, Lijun Yi, Tingfeng Ma, Ji Wang, Heung Soo Kim In this study, the relaxation of free edge stresses in viscoelastic composite laminates is investigated by means of a stress function based viscoelastic model. A linear viscoelastic model using Prony series is adopted for time-dependent material behavior. The stress functions are taken from the Lekhnitskii stress functions and expressed in terms of in-plane stress functions and out-of-plane stress functions, where the out-of-plane stress functions are assumed as a combination of harmonic and hyperbolic functions for developing a Ritz-type solution procedure. By enforcing the complementary virtual work, the fourth order and second order coupled differential equations are obtained and further solved by a standard eigenvalue problem. The benefit of stress function based approach is not merely computationally efficient and accurate. The stress boundary conditions can also be strictly satisfied at the free edges since they are prescribed in the assumed functions. Finally, some of the results will be given for discussion considering different layup stacking sequences. It can be found that by using the present method and Prony series, the relaxation effect on the free edge stresses can be clearly observed and well simulated for the viscoelastic laminates under uniaxial tensile load.
  • Effect of eccentricity on retrofitting efficiency of basalt textile
           reinforced concrete on partially damaged masonry columns
    • Abstract: Publication date: Available online 23 October 2019Source: Composite StructuresAuthor(s): Jiyang Wang, Chenglin Wan, Qiang Zeng, Linghua Shen, Muhammad Akbar Malik, Dongming Yan Retrofitting of damaged and/or ancient masonry structures is of significant importance to increase their structural safety. In this study, a retrofitting technique of basalt-textile-reinforced concrete (BTRC) was used to repair partially damaged rectangle masonry columns, and the repairing efficiency was assessed by different parameters. Compression tests with different eccentricities were conducted to explore the mechanical behaviors of initial and BTRC retrofitted masonry columns. The data in terms of crack patterns, load-displacement curves, peak load, ductility and longitudinal strains were analyzed and discussed in depth. Results show that BTRC retrofits can substantially improve the load carrying capacity and ductility of the partially damaged masonry columns under different eccentric loads that display different damage characteristics. The uniaxial constitutive (NTR-PP, NTR-PB and Sargin) models of masonry predict a relatively safe bearing capacity of BTRC-confined columns under eccentric loadings. This BTRC retrofitting technique with the features of cheap, easy-to-construct, long durability and environmental friendliness shows promising potentials in engineering applications. The findings of this study provide an effective way for repairing ancient and/or damaged masonry structures with BTRC.
  • Parametric Study of a Fibrous Energy Absorbing Material under Impact Shear
    • Abstract: Publication date: Available online 22 October 2019Source: Composite StructuresAuthor(s): Jared Correia, Vijaya Chalivendra, Yong Kim A comprehensive experimental impact characterization study of novel impact energy absorbing (IEA) materials under impact shear loading is conducted. Electro-flocking process is employed to fabricate the novel fiber based padding materials, also known as flocked energy absorbing materials (FEAM). FEAM IEA panels are prepared by flocking 1 to 3 mm long, 6 to 60 denier nylon fibers onto a planar polyester fabric sheet. The impact energy absorption under combined pre-compression loading and shear impact loading is investigated using a custom built guided weight drop tower along with a specially designed pre-compression and shear loading fixture for this study. A parametric study is performed where the effect of fiber material properties such as flock fiber length, diameter and flock density (number of flock fibers per area) on IEA is investigated and they are later compared with that of Vinyl Nitrile (VN) foam materials. Padding material based on FEAM configurations showed remarkable improvement when compared directly to VN foam with a 135% increase in shear strain energy density for the high impact velocity loading condition. Additionally, for low velocity impact conditions, the FEAM based padding materials out performed with a 49% increase in shear strain energy density as compared to VN foam.
  • Overload Damage Mechanisms of GFRP-RC Beams Subjected to High-intensity
           Low-velocity Impact Loads
    • Abstract: Publication date: Available online 22 October 2019Source: Composite StructuresAuthor(s): Zein Saleh, M. Neaz Sheikh, Alex Remennikov, Abheek Basu This paper investigates the overload capabilities and damage mechanisms of Glass Fiber Reinforced Polymer (GFRP) bar reinforced concrete beams subject to high-intensity low-velocity impact loads. The overload condition of the beam is defined as the capability of the beam to sustain input impact energy exceeding its quasi-static energy absorption capacity. Nine GFRP bar reinforced concrete (GFRP-RC) beams were tested under three levels of increasing input impact energy. The shear capacities of the beams were varied by using three spacings of the shear reinforcement. The midspan deflection histories, impact loads, reaction forces, and accelerations of the beams were measured. The crack patterns and failure modes were recorded and analyzed using a high-speed video camera. It was found that the beam shear capacity significantly influenced the type of cracks and the development of cracks under increasing levels of impact energy. Flexural and flexure-shear cracks were observed in the beams with higher shear capacities whereas shear cracks were observed in the beams with lower shear capacities. It was also found that higher beam shear capacities led to reduced residual midspan deflections and higher residual load carrying capacities of the beams. Design recommendations are provided for GFRP-RC beams subjected to high-intensity low-velocity impact events.
  • Design and experimental tests on hydraulic actuator made of composite
    • Abstract: Publication date: 15 January 2020Source: Composite Structures, Volume 232Author(s): Luigi Solazzi The goal of this research is to design, implement and then perform experimental analyses on a hydraulic actuator made of innovative materials such as composite material (carbon fibers and epoxy resin) and the aluminium alloy under high pressure. The cylinder tube is made of an aluminium alloy tubular element wrapped in a composite material; the piston rod is made of composite material and the ends, the attachments and the flanges are made of aluminium alloy. The sizing of the cylinder tube, being a multilayer component under internal pressure, was performed by developing a new theory. Then, a series of numerical finite element analyses were carried out. After the construction of the component, the next phase is experimental tests also made by applying numerous strain gauges to the actuator. The experimental results confirmed the results obtained through analytical and numerical methods. The hydraulic actuator is made up of a composite material and aluminium alloy. The hydraulic actuator made of composite material and aluminium alloy, has a weight of about 12% of the one in a classic structural steel and seems to be a very good result for a continuous lightening of the structural components of the machine.
  • Ultra-light release device integrated with screen-printed heaters for
           CubeSat’s deployable solar arrays
    • Abstract: Publication date: 15 January 2020Source: Composite Structures, Volume 232Author(s): Dou Zhang, Liwu Liu, Jinsong Leng, Yanju Liu Deployable solar arrays can improve the potential utilization of CubeSats by generating sustainable energy. This paper presents an ultra-light release device integrated with screen-printed heaters to latch and release CubeSat’s solar arrays in the sequence of structure and material design, fabrication, and experimental verification. Finite element analysis of interference fit gives the locking force and maximum Von Mises stress variation with the interference and thickness, which provides the selection basis for geometrical parameters of the release device. Tensile and fracture toughness tests have been conducted to verify improved toughness for spandex fiber reinforced shape memory polymer composites (SMPCs). And the fine denier fiber shows a better toughness improvement performance. DMA tests have been performed to give the temperature sensitivity of the materials. Besides, locking forces obtained from finite element analysis and experiments show good consistency. Moreover, recovery tests confirm the release device with good shape recovery properties and excellent adaptability to energizing conditions. Finally, experiments on a CubeSat prototype qualify the release device with good feasibility, reliable locking performance and satisfactory reusability. This work is expected to provide an effective miniaturized hold-release mechanism for deployable structures.
  • Seismic evaluation of ordinary RC buildings retrofitted with externally
           bonded FRPs using a reliability-based approach
    • Abstract: Publication date: 15 January 2020Source: Composite Structures, Volume 232Author(s): Mohammad Ali Mahdavipour, Abolfazl Eslami, Pierre Jehel Despite the extensive literature on reinforced concrete (RC) members retrofitted with fiber-reinforced polymer (FRP) composites, few studies have employed a reliability-based approach to evaluate the seismic performance of RC buildings in terms of their collapse capacity and ductility. In this study, the performance of a poorly-confined RC building structure is investigated for different FRP retrofitting schemes using different configurations and combinations of wrapping and flange-bonded FRPs, as two well-established techniques. A nonlinear pushover analysis is then implemented with a computational reliability analysis based on Latin Hypercube Sampling (LHS) to determine the collapse capacity and ductility of the case-study structure. The variations in material properties and applied loads are examined using a rational probabilistic procedure. The results demonstrate the effectiveness of the reliability approach as it is capable of providing reliable and accurate comparisons between the retrofitting schemes implemented. In addition, the failure modes of the original and retrofitted frames are scrutinized for a more detailed study. It was found that the failure mode of the case-study building is remarkably dependent on the variations of both the input parameters and the adopted retrofitting scheme.
  • On torsion of nonlocal Lam strain gradient FG elastic beams
    • Abstract: Publication date: Available online 16 October 2019Source: Composite StructuresAuthor(s): R. Barretta, S. Ali Faghidian, F. Marotti de Sciarra, R. Penna, F.P. Pinnola The nonlocal strain gradient theory of elasticity is the focus of numerous studies in literature. Eringen’s nonlocal integral convolution and Lam’s strain gradient model are unified by a variational methodology which leads to well-posed structural problems of technical interest. The proposed nonlocal Lam strain gradient approach is presented for functionally graded (FG) beams under torsion. Static and dynamic responses are shown to be significantly affected by size effects that are assessed in terms of nonlocal and gradient length parameters. Analytical elastic rotations and natural frequencies are established by making recourse to a simple solution procedure which is based on equivalence between integral convolutions and differential equations supplemented with variationally consistent (but non-standard) nonlocal boundary conditions. Effects of Eringen’s nonlocal parameter and stretch and rotation gradient parameters on the torsional behavior of FG nano-beams are examined and compared with outcomes in literature. The illustrated methodology is able to efficiently model both stiffening and softening torsional responses of modern composite nano-structures by suitably tuning the small-scale parameters.
  • Composite materials from totora (Schoenoplectus californicus. C.A. Mey,
           Sojak): Is it worth it'
    • Abstract: Publication date: Available online 14 October 2019Source: Composite StructuresAuthor(s): Petra Hýsková, Milan Gaff, Juan Fernando Hidalgo-Cordero, těpán Hýsek Totora (Schoenoplectus californicus. C.A. Mey, Sojak) is an annual-cycled macrophyte from the Cyperaceae family that has been used by indigenous people of the Americas for more than 500 years to produce a wide range of objects from handicrafts to boats and huts. In this study, the hot-pressing process was applied to produce boards from totora particles without added adhesives. First, the physical and mechanical properties of totora binder-free boards are described. Secondly, several factors that influence the properties of totora boards are taken into account. However, is it worth it to produce such boards' In this paper, the reasonability of potential production of these boards is considered from a complex point of view. Although totora shows several benefits such as its fast-growth rate, high dry matter productivity, and potential environmental benefits; the water uptake (92% – 341%), thickness swelling (75% – 227%) and internal bonding (18 kPa – 85 kPa) of the binderless boards made with the parameters described in this study could not comply with current standards. Further research on treatments or different production parameters can lead to better properties.
  • Virtual element method for computational homogenization of composite and
           heterogeneous materials
    • Abstract: Publication date: Available online 14 October 2019Source: Composite StructuresAuthor(s): Marco Lo Cascio, Alberto Milazzo, Ivano Benedetti In this study, a two-dimensional multi-region framework, based on the use of the Virtual Element Method (VEM), is developed for computational materials homogenization and applied to different classes of widely employed heterogeneous materials. The VEM has recently emerged as a powerful generalisation of the Finite Element Method capable of dealing with very general polygonal mesh elements, including non-convex or highly distorted elements. Such features are appealing for the treatment of problems whose analysis domains present complex or statistical morphological features, which would generally require careful and time-consuming mesh/data preparation and regularization. In this work, the lowest-order VEM for two-dimensional elastostatics is employed for the homogenization of polycrystalline materials and unidirectional fibre-reinforced composites. In both cases, artificial micro-morphologies are usually generated resorting to automatic algorithms aimed at approximating/reproducing the statistical microscopic features of real materials. In such a context, the likely presence of morphological irregularities, and subsequent mesh distortions, usually requires caution and the employment of sophisticated mesh regularization procedures. The study demonstrates how the inherent features of the VEM can be conveniently exploited for such classes of problems, as the method allows the relaxation of the requirements on the mesh quality, yet providing accurate numerical results.
  • Investigation of curing deformation behavior of curved fiber metal
    • Abstract: Publication date: Available online 14 October 2019Source: Composite StructuresAuthor(s): Lu Che, Guodong Fang, Zengwen Wu, Yunfei Ma, Jiazhen Zhang, Zhengong Zhou To keep the size and shape accuracy of fiber metal laminates (FMLs) with an initial curvature during manufacturing, curing deformation behavior is investigated by using analytical, numerical and experimental methods. Based on Eckstein’s theory, an analytical model considering slippage effect between metal layer and fiber layer is developed to study the warping deformation modes of curved FMLs after curing process. The warping displacements of the curved FMLs predicted by the analytical method are in good agreement with the finite element results and experimental data. The final equilibrium configurations of the curved FMLs can be captured by using the analytical method, which can guide the size and shape control for FMLs. The effect of the side length, initial curvature radius and stacking sequence on the curing deformation characteristics of curved FMLs is studied. The curing deformation mechanisms of the curved FMLs with [Al/0/90/Al] and [Al/90/0/Al] stacking sequences are also illustrated from the perspectives of force and total strain energy.
  • Modelling Distinct Failure Mechanisms in Composite Materials by a Combined
           Phase Field Method
    • Abstract: Publication date: Available online 14 October 2019Source: Composite StructuresAuthor(s): Peng Zhang, Yaoqi Feng, Tinh Quoc Bui, Xiaofei Hu, Weian Yao A numerical computational framework that combines a phase field model (PFM) and cohesive element (CE) for modelling progressive failure in composite material is proposed. In this setting, cracks in single material and the interface are captured separately by using the PFM and CE. A unified PFM that incorporates general cohesive softening laws is adopted for quasi-brittle fracture process. An energy split scheme is used to prevent material cracking under compressive state. The irreversibility of the damage evolution is enforced by introducing a history related energy density. The compatibility issue between the CE and PFM is considered for accurately capturing complicated failure mechanisms in composite. The developed approach is implemented into commercial software ABAQUS through user-defined subroutine element (UEL). Validation is made by modelling an experiment on delamination migration of a cross ply composite. Failure mechanisms including delamination, matrix crack, and location of delamination migration that observed in the experiment are all well captured. Moreover, the importance of considering the compatibility between CE and other numerical methods is discussed through a complementary modelling.
  • Carbon/Glass hybrid composite laminates in vinylester resin: bending and
           low velocity impact tests
    • Abstract: Publication date: Available online 14 October 2019Source: Composite StructuresAuthor(s): I. Papa, L. Boccarusso, A. Langella, V. Lopresto Composite laminates with different stacking sequences of woven carbon and glass fibre layers in hybrid configurations were manufactured by vacuum resin infusion. The effect of stacking sequence and hybridisation on the flexural properties and impact damage mechanisms were widely studied. The performances were also studied to investigate the effect of the stacking sequence and the hybridisation in an attempt to compare the results from the literature on traditional composite laminates. Bending tests were carried out in three-point configuration, and the failure mechanism was investigated by visual inspection. Impact tests were carried out at penetration and different energy values to study the impact behaviour by evaluating the external and internal damage evolution. At this scope, indentation measurements were carried out by a confocal microscope, whereas the UltraSound technique investigated the delamination. The data obtained from the different configurations were compared at the aim to individuate the best one. The results were then compared with traditional composite laminates to highlight the advantages of the hybridisation. A strong relevance of the stacking sequence in the design to meet specific requirements was observed in both impact and flexural behaviour.
  • Shear strength of bonded joints of carbon fiber reinforced plastic (CFRP)
           laminates enhanced by a two-step laser surface treatment
    • Abstract: Publication date: Available online 12 October 2019Source: Composite StructuresAuthor(s): Yingxi Xie, Binbin Yang, Longsheng Lu, Zhenping Wan, Xiaokang Liu The apparent shear strength of single-lap bonded joints of carbon fiber reinforced plastic (CFRP) can be enhanced by laser surface treatment. In this work, a two-step laser surface treatment was used to improve the single-lap bonded joint performance of CFRP-laminates. STEP-1, the resin at the outer surface of laminates was completely removed by an optimal laser etching process to provide neat carbon fiber fabric. STEP-2, the as-obtained exposed carbon fiber fabric was further irradiated to produce a series of mini-grooves on its surface. Laser scanning parameters, i.e., spot distance, scanning angles, groove distance and patterns, were investigated to analyze their effects on the morphologies of generated grooves. Single-lap shear tests were also carried out to assess the mechanical performance of these laser processing bonded joints. Experimental results indicated that crossed grooves significantly enhanced the shear strength of the CFRP-laminates. Failure morphologies of shear tests were observed to analyze the strengthening mechanism of grooved-CFRP by laser surface treatment. Using optimal processing parameters during laser surface treatment, the apparent shear strength of single-lap bonded joints of CFRP-laminates reached 18.58 MPa, implying a 40.8% enhancement compared with smooth laminates.
  • Research on the Tension Damage Behavior of Sandwich Composite L-joints:
           Experiment and Simulation
    • Abstract: Publication date: Available online 12 October 2019Source: Composite StructuresAuthor(s): Qin Kai, Renjun Yan, Wei Shen, Yaoyu Hu This article studies the failure process of Composite Sandwich L-joints under tension load. Test results show that damage has already taken place well before the loading force reaches the maximum. The failure process is divided into three stages based on the damage initiation force and damage expansion force identified through test data. A new failure criterion is proposed to describe the behavior of the laminate skin. The application of this criterion requires merely common engineering parameters. Simulation result using this new criterion matches both the failure load and the damage process of the experiment, while simulation using other mainstream criteria report much lower ultimate forces.
  • Effects of braiding architectures on damage resistance and damage
           tolerance behaviors of 3D braided composites
    • Abstract: Publication date: Available online 12 October 2019Source: Composite StructuresAuthor(s): Zhang Di, Zheng Xitao, Zhibang Wang, Wu Tianchi, Ahmed Sohail The primary goal of this research is to present a systematic study on the damage resistance and damage tolerance behavior of three-dimensional (3D) braided composites. Therefore, the low velocity impact (LVI) and compression after impact (CAI) tests of 3D braided composites with eight different braiding architectures and a traditional two-dimensional (2D) laminated composite were carried out. The transient impact force response demonstrates that for 3D braided composites, fiber and matrix work as a whole to withstand impact loads and exhibit a progressive failure process, which is a very different phenomenon from the 2D laminates. The damage morphologies of 3D braided composites are obviously different, for 3D four-directional and 3D five-directional composites the damage patterns are in fusiform shape, and in the case of 3D six-directional and 3D seven-directional braided composites, damage patterns exhibit cross-shape. The energy absorption rates of 3D braided composites are 3.53-7.6% lower than 2D laminate, which means less impact energy has been dissipated by matrix and fiber damage. The comparison of LVI damage parameters and CAI shows that 3D5d-A has better damage resistance and damage tolerance.
  • Influence of transcrystalline layer on finite element mesoscale modeling
           of polyamide 6 based single polymer laminate composites
    • Abstract: Publication date: Available online 12 October 2019Source: Composite StructuresAuthor(s): Shafagh.D. Tohidi, Ana Maria Rocha, N. Dourado, Mohammadali Rezazadeh, Nguyen T. Quyen, Andrea Zille, Stefan Hesseler, Thomas Gries, Nadya V. Dencheva, Zlatan Dencheva This study presents a novel approach for finite element modeling of the elastic behavior of a plain-woven reinforced single polymer laminate composites (WSPC) based on polyamide 6 (PA6). These composites are produced via compression molding of PA6 woven textile structures that are powder-coated by anionic PA6 microparticles. Morphological and structural analysis complemented by electron microscopy, image processing and X-ray diffraction suggest the presence of transcrystalline layer (TCL) at the matrix-reinforcement interface. Having in mid this experimental fact, a novel procedure is developed for finite level discretization of TCL in the representative volume element (RVE) during tensile straining. The procedure correlates the material properties with the overall load applied, thus adequately modelling the tensile behavior of the WSPC based on the constituent materials. The stress field along the elements of the RVE model is studied while the tensile loads were applied in two principal directions. A good agreement between the real mechanical behavior and that calculated based on the model was demonstrated.
  • A critical review of available composite damage growth test data under
           fatigue loading and implications for aircraft sustainment
    • Abstract: Publication date: Available online 12 October 2019Source: Composite StructuresAuthor(s): L. Molent, A. Haddad With growing interest in moving towards a slow-growth design or in-service sustainment basis for aircraft composite and bonded structures, there is a need to establish whether the growth of typical damage in such structure under fatigue loading is systematic and therefore predicable. To this end this paper presents test data from the available literature and draws some general conclusions from this review. The results, which were mainly from aerospace grade carbon/epoxy material systems support the hypothesis that damage growth in composites is a function of applied fatigue cycles and evolves systematically. Also, simple damage metrics retrievable from field level non-destructive inspection are able to capture some, and possibly in some cases, the majority, of the physical nature of the evolution. The work herein sets the foundation for the development of deployable bridged-scale assessments of the effect of damage on the residual static strength and durability performance of composite aircraft structure to support airworthiness decision making.
  • Investigation on In-plane Shear Behavior of Large-Size Composite Plates
           with Multi-bolt Joints
    • Abstract: Publication date: Available online 12 October 2019Source: Composite StructuresAuthor(s): Zhang Fa, Hu Zhendong, Gao Limin, Wan Yumin, Jin Limin, Jia Xiwen, Wang Ke, Ma Qian This paper aims to investigate the in-plane shear behavior of large-size composite plates with multi-bolt joints. A mechanical joint structure and an universal fixture were designed and in-plane shear tests were carried out. The distributed strain gauges were used to monitor the mechanical response and ultimate bearing capacity. The failure areas and failure modes of mechanical connections were studied by ultras-scanning. A non-linear finite element model (FEM) based on 2D shell element mesh was developed to predict the load distribution and failure modes of bolt joints between composite and titanium alloys. The results show that the shear failure load reaches 365.95 kN. The shear failure occurs on the outside edges of composites plate, and the delamination extends to the vicinity of the fixture bolts. The new FEM that requires very small computational cost can evaluate the structure strength and predict destruction area. The deviation between the predicted shear failure responses and the testing results is less than 10%. The failure mode and location are consistent with the testing results, which verifies the validity of the finite element model. It suggests that this model is applicable on large scale structures and suitable to use in conjunction with iterative schemes.
  • A unified Fourier series solution for vibration analysis of FG-CNTRC
           cylindrical, conical shells and annular plates with arbitrary boundary
    • Abstract: Publication date: Available online 12 October 2019Source: Composite StructuresAuthor(s): Bin Qin, Rui Zhong, Tiantian Wang, Qingshan Wang, Yongge Xu, Zehua Hu This research paper presents a unified Fourier series solution to solve the vibration problem of functionally graded carbon nanotube-reinforcement composite (FG-CNTRC) cylindrical shells, conical shells and annular plates subjected to general boundary conditions, so as to enrich the existing research results on FG-CNTRC structures. Utilizing a micro-mechanical model based on the developed rule of mixtures, the effective material properties of the FG-CNTRC structures which is strengthened by single-walled carbon nanotubes (SWCNTs) are scrutinized. The first-order shear deformation theory (FSDT) and the virtual boundary method are applied to achieve the energy expressions of FG-CNTRC structures. On the basis of that, the unified Fourier series solution in conjugation with the modified Fourier series and Ritz method, is utilized to receive characteristic equation of the structural vibration. The correctness, convergence and several advantages of the present methodology are verified by numerous numerical examples. Furthermore, some novel numerical results, including the vibration results of FG-CNTRC cylindrical shells, conical shells and annular plates accompanied with classical boundary, elastic boundary, classical-elastic mixed boundary and parameterized results of structure and material parameters, will be presented for future researchers.
  • On the modeling of nonlinear supersonic flutter of multibay composite
    • Abstract: Publication date: Available online 11 October 2019Source: Composite StructuresAuthor(s): T.A.M. Guimarães, F.D. Marques, A.J.M. Ferreira Panel flutter modeling and analysis had regained importance since the mid-’90s. More recently, the idea of considering the mutual influence of adjacent panels in the flutter problem was revisited in studies of panels with multiple supports. These so-called multibay arrangements present flutter mechanism susceptible to jump phenomenon in the Hopf bifurcation diagram. Alternative methods to reduce the computational costs of multibay flutter analysis are desired. The authors propose in this work a comparative study on the supersonic multibay composite panel flutter between the finite element and Rayleigh-Ritz models. The aim is to show how good is the Rayleigh-Ritz approach to match the finite element model results, mainly when the jump phenomenon is present. By adopting the same hypotheses for thin-walled plates, relatively large geometric displacements through the von Kármán strain-displacement relations and first-order piston theory the finite element and Rayleigh-Ritz methods were used to attain the respective modeling. A specific symmetric laminate is used, and results from the literature are used to compare the results and to verify the ability of both methods. Furthermore, the computational gain in using the Rayleigh-Ritz compared with the finite element is discussed, thereby ensuring its potential to other analyses, e.g., in optimization schemes.
  • Flexural performance of corroded continuous RC beams rehabilitated by
    • Abstract: Publication date: Available online 11 October 2019Source: Composite StructuresAuthor(s): Mei-ni Su, Chaoqun Zeng, Wan-qian Li, Ji-Hua Zhu, Wei-hao Lin, Tamon Ueda, Feng Xing Continuous reinforced concrete (RC) beams are popular structural components. However, RC structures in corrosive environments can be degraded due to steel reinforcement corrosion. In this study, a dual-functional intervention method, i.e., impressed current cathodic protection and structural strengthening (ICCP-SS), is adopted to repair degraded beams. The carbon fabric-reinforced cementitious matrix (C-FRCM) composite serves dual functions in the intervention method. The effects of reinforcement corrosion, cathodic protection and the C-FRCM strengthening system on the behaviors of continuous beams should be investigated. This study provides experimental data on continuous RC beams rehabilitated by ICCP-SS in corrosive environments and investigates the structural responses, moment redistributions and design rules of these beams. The electrochemical monitoring results showed that steel reinforcements in continuous beams under corrosive environments are successfully protected. Five-point bending test results showed that beams strengthened with C-FRCM composites have higher yielding loads and ultimate loads than corroded beams without protection. Comparison of the predicted and measured moment capacities at the central support and midspan showed that the design methods generally underestimate the moment capacities of unstrengthened sections and overestimate those of strengthened sections.
  • Hydrothermal Effect on Bi-stability of Composite Cylindrical Shell
    • Abstract: Publication date: Available online 10 October 2019Source: Composite StructuresAuthor(s): Yaopeng Wu, Kaixuan Gao, QianQian Ren Bi-stable composite cylindrical shells have attracted many attentions due to their lightness, simple structure, high packaging efficiency, high specific strength and stiffness. However, the anti-symmetric cylindrical shell is susceptible to the effect of ambient temperature and humidity. In this paper, an analytical model of shell structure considering hydrothermal effect was built, and its strain energy expressions were derived. Based on the minimum energy principle, the effects of moist and heat on the bi-stability of cylindrical shell structure were analyzed. In addition, the finite element model of the anti-symmetric cylindrical shell was established to simulate its stable configurations. This study could provide reference for the practical application of bi-stable structure.
  • Mechanical Integrity of Friction-riveted Joints for Aircraft Applications
    • Abstract: Publication date: Available online 10 October 2019Source: Composite StructuresAuthor(s): N.Z. Borba, B. Kötter, B. Fiedler, J.F. dos Santos, S.T. Amancio-Filho The predictability of damage evolution is a challenge for mechanical joints of composite structures due to the highly nonlinear material behavior. In this study, friction riveting was investigated as an alternative joining technology for composite laminates by analyzing experimentally the joint mechanical behavior under different loading scenarios. The failure and fracture micro-mechanisms of composite laminate single lap joints were studied under quasi-static and cyclic loading. The joints failed mainly by rivet detachment from the composite hole, followed by adhesive/cohesive failure of the squeezed material, and rivet pull-through failure. Despite lower quasi-static strength of friction-riveted joints (6.2 ± 0.3 kN) compared to reference bolted joints (8.7 ± 0.2 kN), their fatigue life was higher by 88%. The main improving contributions were: the squeezed material, working as an adhesive between the composite parts and an additional fracture micro-mechanism, and the absence of clearance at the rivet-composite interface, which promoted an improved load transfer between the joined parts.
  • Experimental and numerical analysis of unfolding failure of L-Shaped CFRP
    • Abstract: Publication date: Available online 10 October 2019Source: Composite StructuresAuthor(s): P. Journoud, C. Bouvet, B. Castanié, F. Laurin, L. Ratsifandrihana Highly curved laminated parts are used at the junction between two different perpendicular panels on aircraft primary structures. Usually, these laminates fail by delamination due to a bending moment, which appears when the part is loaded. The bending moment tries to flatten the part and out-of-plane tensile stresses are generated in the curvature. This failure is traditionally called unfolding failure. The modelling strategy called the ‘Discrete Ply Model’ (DPM) is used to simulate four-point bending tests on L-angle specimens. Experimental results of four point bending tests carried out at ONERA are used to validate the approach. Four different stacking sequences with the same thickness are taken into consideration in this study. In a second part, a sensitivity analysis on frictional coefficient, intralaminar matrix cracking, transverse tensile and shearing strength, and critical energy release rate in modes I and II is performed numerically and provides an original explanation of the failure scenario and the most influential parameter.
  • Compression Behavior of Large-Scaled Cylindrical GFRP Chimney Liner
    • Abstract: Publication date: Available online 10 October 2019Source: Composite StructuresAuthor(s): Shi Cheng, Peng Feng, Xinmiao Meng, Zhiyuan Li, Jike Du As a pivotal anti-corrosion structure in the wet flue gas desulfurization system, the huge filament-wound GFRP (glass fiber-reinforced polymer) tuber is often employed as the chimney liner. However, the study on its mechanical properties is rare. Three large-scale stiffened cylindrical GFRP chimney liner segments were tested under the axial compression, including an integrated filament-wound chimney liner specimen with two ring stiffeners, a specimen with two ring stiffeners cut into two segments and joined by a hand-wound technique, and a specimen with an outside ring bracket. The failure modes, load-displacement relationships, variation of strains during the loading process, were acquired by test. The effects of ring stiffeners on the mechanical behavior, service reliability of the joint between the two segments of the chimney liner, and the reliability of the ring bracket were examined. Comparisons between theoretically calculated stiffness and experimentally measured stiffness were discussed. Finally, finite element analysis was performed to examine the failure modes and axial load-displacement behavior of the investigated chimney liners. Different ranges of diameter to thickness ratios and load eccentricity values were selected to examine their effects on the mechanical behavior of chimney liners. Finally, suggestions on the design of chimney liner structure were given.
  • On lateral compression of circular aluminum, CFRP and GFRP tubes
    • Abstract: Publication date: Available online 10 October 2019Source: Composite StructuresAuthor(s): Shunfeng Li, Xiao Guo, Qing Li, Dong Ruan, Guangyong Sun Thin-walled structures made of lightweight materials, e.g. aluminum, fiber reinforced composites, have been increasingly used as energy absorption structures in vehicles. This work aimed to characterize the lateral crushing behaviors of circular aluminum, glass fiber reinforced plastics (GFRP) and carbon fiber reinforced plastics (CFRP) tubes with different geometric configuration such as diameter-to-thickness (D/T) ratio or thickness. In the experimental investigation, four different D/T ratios varied from 10.78 to 48.02 was considered here for the aluminum, GFRP and CFRP tubes. Crashing behaviors such as force-displacement curves, deformation histories, and crushing force was quantified. The experimental results revealed that the load carrying capacities, energy absorption (EA) and specific energy absorption (SEA) of the circular tubes decline with the increase in the D/T ratio. It was found that better crashworthy characteristics of thicker composites, with a smaller D/T ratio, is due to the more favorable failure modes occurring throughout lateral compression. The lateral crashworthy performance of the GFRP tubes was marginally better than the CFRP counterparts. Due to ductile behavior of aluminum tubes and brittle behavior of composites, aluminum tubes showed much better lateral crashworthiness than that of the composite counterparts. Moreover, with the increase in the D/T ratio, aluminum tubes exhibited greater advantage on crashworthiness than the composite tubes. On the basis of the experimental data, explicit finite element analysis was further conducted for modeling the lateral crushing behavior of aluminum, GFRP and CFRP tubes. The numerical results were in good agreement with the experimental data, demonstrating the validity of these finite element (FE) models in predicting lateral crushing responses of aluminum, GFRP and CFRP tubes. The proposed FE models can be exploited to further study similar thin-walled metal and composite structures for design optimization.
  • Finite Element Analysis of the Longitudinal Half Fixed Beam method for
           mode III characterization
    • Abstract: Publication date: Available online 10 October 2019Source: Composite StructuresAuthor(s): Jorge Bonhomme, Victoria Mollón, Jaime Viña, Antonio Argüelles In this work, the Longitudinal Half Fixed Beam test (LHFB) for mode III characterization is analysed by means of Finite Element Analysis (FEA) and optical microscopy. The obtained results were compared with experimental data and analytical formulations obtained in previous works. The objective of this study is to determine the energy distribution across the crack front and to understand the micromechanics that give rise to the delamination failure in unidirectional carbon/epoxy composites.It was found that for samples with long initial crack lengths (i.e. a0=30 mm), pure mode III takes place in the central part of the delamination front. Nevertheless, these samples present a significant contribution of mode II at the edges of the specimen. As a0 decreases, pure mode III increases in extension across the delamination front and mode II decreases at the sample edges. When the initial crack length (a0) is quite small, the sample presents pure mode III practically on the entire length of the crack front. Nevertheless, when the initial crack is very small, the applied force exercises a local influence on the tip of the crack at the edge of the sample and mode III distribution loses its uniformity across the crack front.The concordance between the analytical results and the numerical results obtained by the Finite Element Method (FEM) was variable depending on the length of the crack and if the comparison was made with GIII or GT as reference.Intralaminar cracks at approximately 45° with respect to the midplane were observed in planes perpendicular to the direction of delamination propagation (planes perpendicular to the fibre direction). Other authors also found this type of intralaminar cracks in other mode III test configurations.
  • Damage detection via embedded sensory particles – effect of
           particle/matrix interphase properties
    • Abstract: Publication date: Available online 9 October 2019Source: Composite StructuresAuthor(s): M.M. Mirsayar, D.J. Hartl Supported by recent studies, a crack interior to the host material will cause an especially strong stress concentration and thus can be detected by monitoring or sensing the localized changes in the magnetic properties of the particles in metallic composites. Using finite element analysis calibrated from the experiments, this work investigates the effects of material properties and thickness of the particle/matrix interphase on the phase transformation response of embedded sensory particles in the vicinity of a crack existing in the host matrix. Depending on the interphase elastic and cohesive properties, its thickness, and the operational temperature, which is known to delay or promote martensitic transformation, it is found that interphase damage may occur at stress levels lower than that needed to initiate phase transformation in MSMA particles. Such a response would mitigate the degree to which the particle transforms and reduces particle sensitivity. The effect of particle position relative to the crack tip on interphase damage and particle transformation response is studied via the full factorial design of experiments. To assess the true feasibility of the technique, the average change in magnetic permeability in the vicinity of the particle given constant applied magnetic and applied stress fields is evaluated.
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